U.S. Pat. No. 4,039,281 discloses a process for the production of fur skins in which the skins at a water content of 30 to 80 percent by weight are treated with tanning chemicals present in an organic solvent which is immiscible with water.
This process permits a sharp reduction in the amount of waste waters which are either harmful or difficult to convert to harmless form, and offers other advantages, among them a considerable saving in chemicals. In the production of crude skins worked in the round (i.e., not slit at the belly or back), which are treated in the solvent medium with the hair side turned inward, the skins can however be freed only very slowly, incompletely and with great effort of the solvent medium contained therein or adhering thereto. It is therefore necessary to remove the skins freed by airing of the solvent medium only in the fur leather from the machine with a protective mask, and to turn inside out under a ventilated hood. In the subsequent milling step, the solvent medium can be removed also from the hair, whereupon the pelts are again turned and moved to a kicking processor.
It is an object of the invention to avoid the aforementioned disadvantages without sacrificing the advantages achieved by the process according to U.S. Pat. No. 4,039,281, particularly the solution of the waste water problems.
This object is achieved by treating the skins at a water content of 30 to 80 percent by weight in an organic, water immiscible, liquid, not very volatile carrier medium with tanning chemicals, and after tanning, and possibly other processing, removing the predominant portion of the carrier medium contained in or adhering to the fur skins by centrifuging or squeezing or other physical force process, with little or no heating.
It has molecular weight found that the aforementioned carrier medium for fur skins can be substituted also in other process steps for the solvent medium prescribed in U.S. Pat. No. 4,039,281. Although particular advantages are obtained in using the organic, water-immiscible, not very volatile (high molecular and high boiling), liquid carrier medium specifically for skins worked in the round (espec. fine (noble) fur skins such as muskrat and mink), it is useful also for other fur skins. Because of its lesser volatility, the mentioned carrier medium requires less equipment outlay and can at least partly take the place of fat-liquoring or kicking if it consists of a suitable mineral oil.
Preferably, the carrier medium consists of high molecular weight hydrocarbons (mineral oils), high molecular weight, chlorinated hydrocarbons (especially liquid chloroparaffins) or high molecular weight esters (fatty oils such as triolein or liquid waxes such as sperm oil). After removal, it can be fed to a tank for re-use. The carrier medium in the tank contains substantially no chemicals. To the extent that it carried along water from the pelts, this settles to the bottom of the tank and can be decanted. Since the amount of decanted water which can contain chemical residues is small, their environmentally neutral disposal entails little cost. Upon repeated re-use of the carrier medium, there will be a gradual accretion of natural fats from the skins, but this has no negative effect on the production process.
In contrast to the use of a solvent medium, the described production process considerably simplifies the treatment of skins worked in the round, since twice-repeated turning is obviated, and the skins can be moved directly to the drying and fat-liquoring or kicking stations after centrifuging of the carrier medium. In summary, the following advantages are obtained:
(1) Health hazards and noxious odors resulting from the use of organic solvents are removed. PA1 (2) The necessarily greater outlay for equipment required by the organic solvent is reduced. PA1 (3) Due to the residues of carrier medium remaining in the skin after centrifuging, the amount of fat-liquor or kicking oil can be reduced. PA1 (4) In the case of skins worked in the round, twice-repeated turning is avoided, whereas this is required when a solvent medium is used in order to remove such solvent medium. PA1 (5) In the case of fine wolled skins, the formation of matting is virtually avoided.